I'm about to wrap up what is (for me) a fairly exciting project on my 240Z, and I thought it would be nice to share, as it's not something I see discussed here very often.
The goal: retain AM radio function in my Series 1.5 (5/71, so series 1 drivetrain and dash, but no hatch vents) 240z, while being able to pair with my phone and stream music over bluetooth.
My materials: a class D one-board amp (bought from a guy who calls them "Shiznit", hence "U_Shiznit" in the wiring diagram), 50Wx2, a handful of relays, a line-level bluetooth board, two Match M5X speakers, and a spare speaker bracket from another 240z.
My modifications: I created a switched output from the Hitachi TM-1081ZB by soldering an additional wire (I chose purple, to differentiate from the existing harness colors) to the switch side of the L10 choke coil (the Hitachi service manual is available online), and then running that out the bottom of the deck through the remaining open hole.
The drawbacks: Limited to 5.25" speakers that fit in the stock hatch locations, I'm not going to win any sound quality or SPL competitions. I also had to crack open my AM unit to add the switched 12V, which can be nerve wracking. Honestly, my Z is pretty loud (2.5" exhaust, triple webers, rumbly cam), so the goal is really just to have intelligible audio in a stealthy package.
Wiring diagram:
Pre-relay testing configuration:
So far, I've only mocked up the connections, but I'm running the wires soon (the entire thing should fit under the lid of the driver's side storage bin) for final installation.